The present invention relates to an alternating to direct voltage converter in form of an integrated circuit comprising on a same substrate at least a first field effect transistor with insulated gate, a current-limiting means feeding said first transistor and a first coupling capacitor connected to the input of said first transistor for controlling said first transistor by said alternating voltage.
Such a converter is provided for the regulating circuit Reg of a quartz crystal oscillator, e.g. for an electronic watch. FIG. 1 shows the circuit diagram of an oscillator comprising a converter according to the present invention. The properly so called oscillator comprises an amplifier A1, a quartz crystal resonator Q and two phase-shifting capacitors C5 and C6. The amplifier A1 is fed by a current source Io like the one described in the U.S. Patent Application Ser. No. 968,902, for maintaining the current of the oscillator at a determined, relatively small value. The regulating circuit Reg of FIG. 1 permits, by acting on the current source Io in function of the amplitude of the alternating voltage of the oscillator to further reduce the power consumption of the circuit. An amplifier A2 receives the relatively small alternating signal of the oscillator and delivers an amplified signal having sufficient amplitude for adequately driving stages normally connected to the oscillator.
From FIG. 2 of the document (1), "ESSCIRC 1976, Toulouse, New analog CMOS IC's based on weak inversion operation, E. Vittoz and S. Fellrath, Centre Electronique Horloger SA, Neuchatel, Switzerland", it is known an amplitude detector or alternating to direct voltage converter comprising a transistor T1 fed by a current source (T2,T6) and further comprising associated elements like R1, R2, C1, C2 and C3. In such a circuit, the resistors R1 and R2 must have a very high impedance, in the order of magnitude of 100 megohms and it is proposed to implement them by back to back polycrystalline diodes. Such diodes can be produced by a particular technology only (Si-gate technology), which considerably limits their possibilities of applications.